US 20060162456 A1
A hat stringer inspection device permits continuous inspection of hat stringers as one or more probes are moved along the length of the hat stringer. Probes may be magnetically coupled to opposing surfaces of the structure, including, for example, where one of the probes is positioned inside the hat stringer and the probes are magnetically coupled across the surface of the hat stringer. The device may be autonomous with a feedback-controlled motor to drive the inspection device along the hat stringer. Magnetic coupling is also used to re-orient the position and/or alignment of the probes with respect to changes in the hat stringer or shapes, sizes, and configurations of hat stingers.
1. A non-destructive inspection apparatus for inspecting a structure, comprising:
a first probe configured for traveling over a first surface of the structure under inspection, the first probe comprising at least one inspection sensor for inspecting the structure as the first probe is moved over the first surface of the structure and at least one magnetic coupling device, wherein the first probe is further configured to span a cross-section of the structure that protrudes from the first surface of the structure; and
a second probe configured for traveling over a second surface of the structure and magnetically coupled to the first probe, the second probe comprising and at least one magnetic coupling device, wherein the probes cooperate by the magnetic attraction between corresponding magnetic coupling devices to correspondingly move the magnetically coupled probes over the respective surfaces of the structure.
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10. A probe for inspecting a structure comprising:
a housing configured for traveling over a first surface of the structure under inspection, and wherein the housing is further configured to span a cross-section of the structure that protrudes from the first surface of the structure; and
at least one inspection sensor carried by the housing for inspecting the structure as the probe is moved over the first surface of the structure.
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21. A method of inspecting a structure comprising:
supporting a first probe on a first surface of the structure and a second probe on an opposed second surface of the structure, wherein the first probe is configured to span a cross-section of the structure that protrudes from the first surface of the structure to form a hat stringer;
positioning the first probe across the hat stringer;
establishing magnetic attraction between the first and second probes such that the first and second probes are drawn toward the first and second surfaces of the structure, respectively;
moving one probe along one surface of the structure which causes the other probe to move along the opposing surface of the structure; and
transmitting inspection signals into and receiving inspection signals from the structure as the probes are moved along the structure.
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The contents of U.S. Pat. No. 6,722,202 and co-pending application Ser. No. 10/752,890, entitled “Non-Destructive Inspection Device for Inspection Limited-Access Features of a Structure,” filed Jan. 7, 2004; application Ser. No. 10/943,135 entitled “Magnetically Attracted Inspecting Apparatus and Method Using a Fluid Bearing,” filed Sep. 16, 2004; application Ser. No. 10/943,088, entitled “Magnetically Attracted Inspecting Apparatus and Method Using a Ball Bearing,” filed Sep. 16, 2004; and application Ser. No. 10/943,170, entitled “Alignment Compensator for Magnetically Attracted Inspecting Apparatus and Method,” filed Sep. 16, 2004, are incorporated by reference.
The present invention relates generally to an apparatus and method for inspecting a structure and, more particularly, to an apparatus and method for non-destructive inspection of limited-access features of a structure.
Non-destructive inspection (NDI) of structures involves thoroughly examining a structure without harming the structure or requiring its significant disassembly. Non-destructive inspection is typically preferred to avoid the schedule, labor, and costs associated with removal of a part for inspection, as well as avoidance of the potential for damaging the structure. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly used in the aircraft industry to inspect aircraft structures for any type of internal or external damage to or flaws in the structure. Inspection may be performed during manufacturing of a structure and/or once a structure is in-service. For example, inspection may be required to validate the integrity and fitness of a structure for continued use in manufacturing and future ongoing use in-service. However, access to interior surfaces is often more difficult or impossible without disassembly, such as removing a part for inspection from an aircraft.
Among the structures that are routinely non-destructively tested are composite structures, such as composite sandwich structures and other adhesive bonded panels and assemblies, such as hat stringers or hat stiffeners made from carbon fiber reinforced and graphite epoxy (Gr/Ep) materials and co-cured or co-bonded hat stringers. In this regard, composite structures are commonly used throughout the aircraft industry because of the engineering qualities, design flexibility and low weight, such as the stiffness-to-weight ratio. As such, it is frequently desirable to inspect composite structures to identify any flaws, such as cracks, voids or porosity, which could adversely affect the performance of the composite structure.
Various types of sensors may be used to perform non-destructive inspection. One or more sensors may move over the portion of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo (PE), through transmission (TT), or shear wave sensor may be used to obtain ultrasonic data, such as for thickness gauging, detection of laminar defects and porosity, and/or crack detection in the structure. Resonance, pulse echo or mechanical impedance sensors may be used to provide indications of voids or porosity, such as in adhesive bondlines of the structure. High resolution inspection of aircraft structure are commonly performed using semi-automated ultrasonic testing (UT) to provide a plan view image of the part or structure under inspection. For example, solid laminates may be inspected using one-sided pulse echo ultrasonic (PEU) testing and composite sandwich structures may be inspected using two-sided through-transmission ultrasonic (TTU) testing. In pulse echo ultrasonic (PEU) testing, ultrasonic sensors, such as ultrasonic transducers, are positioned adjacent to or near one surface of the structure to be inspected. For example, the PEU transducer transmits an ultrasonic signal into the structure under inspection and receives the reflection of the ultrasonic signal from the structure. In through-transmission ultrasonic inspection, paired ultrasonic sensors such as transducers, or transducer and a receiver pairings, are positioned facing the other but contacting opposite sides of the structure. An ultrasonic signal is transmitted by at least one of the transducers, propagated through the structure, and received by the other transducer. Data acquired by sensors, such as PEU and TTU transducers, is typically processed by a processing element, and the processed data may be presented to a user via a display. A data acquisition board and data handling software may be used for collection and display of inspection data, such as displaying the data on a computer monitor as an image representation of the structure under inspection, such as a hat stringer, supplemented with corresponding color and/or graphical data of the inspection to permit examination by a qualified inspector.
Non-destructive inspection may be performed manually by technicians who typically move an appropriate sensor over the structure. Manual scanning requires a trained technician to move the sensor over all portions of the structure needing inspection. Manual scanning typically involves the technician repeatedly moving a sensor side-to-side in one direction while simultaneously indexing the sensor in another direction. In addition, because sensors typically do not associate location information with the acquired data, the same technician who is manually scanning the structure must also watch the sensor display while scanning the structure to determine where the defects, if any, are located in the structure. The quality of the inspection, therefore, depends in large part upon the technician's performance, not only regarding the motion of the sensor, but also the attentiveness of the technician in interpreting the displayed data. Thus, manual scanning of structures is time-consuming, labor-intensive, and prone to human error.
Semi-automated inspection systems have also been developed. For example, the Mobile Automated Scanner (MAUS®) system is a mobile scanning system that generally employs a fixed frame and one or more automated scanning heads typically adapted for ultrasonic inspection. A MAUS system may be used with pulse-echo, shear wave, and through-transmission sensors. The fixed frame may be attached to a surface of a structure to be inspected by vacuum suction cups, magnets, or like affixation methods. Smaller MAUS systems may be portable units manually moved over the surface of a structure by a technician.
Automated inspection systems have also been developed. For example, the Automated Ultrasonic Scanning System (AUSS®) system is a complex mechanical scanning system that may employ through-transmission ultrasonic inspection. An AUSS system can also perform pulse echo inspections, and simultaneous dual frequency inspections. The AUSS system has robotically controlled probe arms that may be positioned, for example, for TTU inspection proximate the opposed surfaces of the structure undergoing inspection with one probe arm moving an ultrasonic transmitter along one surface of the structure, and the other probe arm correspondingly moving an ultrasonic receiver along the opposed surface of the structure. To maintain the ultrasonic transmitter and receiver in proper alignment and spacing with one another and with the structure undergoing inspection, a conventional automated inspection system may have a complex positioning system that provides motion control in numerous axes, such as the AUSS-X system which has motion control in ten axes. Automated inspection systems, and like robotics, however, can be prohibitively expensive. Further, orienting and spacing sensors with respect to the structure, and with respect to one another for TTU inspection, may be especially difficult in conjunction with structures with non-planar shapes, such as the inspection of curved structures and hat stringers. Also, conventional automated scanning systems, such as the AUSS-X system, may require access to both sides of a structure which, at least in some circumstances, will be problematic, if not impossible, particularly for very large or small structures. Furthermore, scanning systems inspect limited areas up to a few meters square.
Accessibility to the structure requiring inspection and to particular features is also an important consideration. Access may be so limited that manual inspection or automated inspection is not possible. For example, the inside of a hat stringer of the fuselage of an aircraft has limited access for inspection, especially far from an end.
An apparatus for inspecting a structure, such as a hat stringer, includes autonomous crawlers coupled to the fuselage to inspect the hat stringers using a feedback-controlled motor to drive the inspection device. The present system is particularly adapted for inspecting composite hat stringers.
Magnetic coupling holds the inspection device on the structure under inspection on opposite sides for through transmission inspection. The first probe of the inspection device rides along the outside of the hat stringer while the second probe rides below the hat stringer or inside the hat stringer. The magnetic coupling along with the configuration of the inspection device keep inspection sensors, such as ultrasonic transducers or x-ray sources and detectors, are aligned to inspect the hat stringer as the inspection device moves along the length of the hat stringer. The magnetic coupling keeps the transducers coupled and in physical contact with the surfaces of the structure. Keeping the transducers coupled to the structure is important to ensure reliable inspection, such as to provide for strong and consistent signal transmission. The design of the inspection device also permits accurate position measurement or sensing along the length of the structure by using an encoder.
Embodiments of the present invention refine general features and functionality of the Remote Access Bondline Inspection Tool (RABIT) as described in U.S. patent application Ser. No. 10/752,890, filed Jan. 7, 2004, for inspecting hat stringers.
The preferred design accommodates variations of different hat stringer design shapes and sizes and part thickness changes, such as axial part thickness variance. For example, a central section and side sections of an interior probe may be arranged to permit the side sections to move to match the angle of the sides of the hat stringer. The probe might be self-adjusting using a spring loading or more sophisticated adjustment means like adjustment slots or jackscrews. Transducers oriented to inspect the corners of the hat stringer will remain aligned with the corners by telescoping a middle section as the hat stringer increases in width. Selection of transducers depends on the type of material and its thickness. Higher frequency transducers usually are used for thinner hat stringer thicknesses.
The present invention will be described more fully with reference to the accompanying drawings. Some, but not all, embodiments of the invention are shown. The invention may be embodied in many different forms and should not be construed as limited to the described embodiments. Like numbers and variables refer to like elements and parameters throughout the drawings.
Embodiments of non-destructive stringer inspection apparatus and methods of the present invention are described with respect to hat stringers, especially composite hat stringers for an aircraft fuselage. However, the apparatus and methods may also be used for similar applications which require non-destructive inspection, including other composite structures with difficult-to-inspect geometric configurations and/or remote locations. Embodiments of hat stringer inspection apparatus and methods may include magnetically coupled probes as described in co-pending application Ser. Nos. 10/943,088; 10/943,135; 10/752,890; or 10/943,170.
Inspection devices can inspect a variety of structures formed of various materials. For devices which transmit magnetic fields through the structure, however, the structure under inspection is preferably non-magnetic, that is, the structure preferably has no magnetic permeability. Such structures include composites such as carbon fiber or graphite reinforced epoxy (Gr/Ep) and non-ferromagnetic metals (e.g. aluminum alloy, titanium alloy, or aluminum or titanium hybrid laminates such as GLARE or Ti/Gr). The surfaces and intermediate septums which collectively define the test article are non-magnetic to allow magnetic coupling between the probes.
Inspecting hat stringers normally requires a one-sided inspection technique, such as pulse echo ultrasonic (PEU) inspection. However, the shapes of hat stringers complicate the inspection. The hat stringer inspection device can perform pulse echo inspection or through transmission ultrasonic (TTU) inspection.
Inspection sensors of a probe may be strategically placed and oriented, such as aiming transducers at the corners or edges of the hat stiffener, to ensure full inspection of the entire hat stringer. Support structures for inspection sensors, also referred to as transducer holders, may be fabricated for specific placement and orientation of inspection sensors corresponding to the intended shapes and sizes of hat stringers. For example, the first inspection probe 80 with transducer holders 84 shown in
Three types of inspection probes are provided. A fixed orientation probe includes a housing that supports any of inspection sensors, contact members, and magnetic coupling devices such that the inspection probe functions as a single, integrated device. A segmented probe decouples the housing that supports any contact members and/or magnetic coupling devices from transducer holders that support the inspection sensors such that the probe is capable of re-orienting the transducer holders and, thereby, any inspection sensors with the shape and structure of the hat stringer under inspection. A partially fixed orientation probe may include hinged sections which permit limited re-orientation of the inspection probe to permit better alignment of inspection sensors or positioning of magnetic coupling devices and/or contact members. These three variations of inspections probes may be used in different combinations depending on the particular circumstances of inspection.
If access is available under the hat stringer at the exterior surface of the fuselage, magnetic coupling through the fuselage wall will hold the first probe on the hat stringer and the second probe against the interior surface of the fuselage, as shown in
At least one probe may include inspection sensors such as a pulse echo sensor, ultrasonic transducer, x-ray source, x-ray detector, encoder, or camera. The ultrasonic transducer may be a 1 MHz immersion transducer from Agfa/Krautkramer of Lewistown, Pa. As shown in
The probes 30, 40 also include contact members 41 such as wheels, bearings, or skids to allow the probes 30, 40 to easily move across surfaces 14, 15 and 16. Each contact member 41 supports the probe 30, 40 at the proper spacing from the surface 14, 15 and 16 and reduces the frictional drag to permit smooth translation of the probe across the surface.
By magnetically coupling the probes 30, 40 to each other on opposing surfaces 14, 15 and 16 of the structure under inspection, either probe may be driven, i.e., moved across the respective surface of the structure under inspection by a translational force, thereby moving the opposing magnetically coupled probe. Each probe 30, 40 includes a housing 34, 44 to carry the various elements of the probe, such as the magnetic coupling devices 42, contact members 41, and inspection sensors 36, 37, 38, 39. The housing may be made, for example, from plexiglass, plastic, or other materials which provide structural support, durability, do not interfere with the inspection method, and are unlikely to damage the surface of the part under inspection such as by scratching the surface upon contact.
A probe 30 may be designed to accommodate hat stringers of different widths and hat stringers that vary in width. A probe 30 may be formed from two sides 46, 48. As the width of a hat stringer increases or when the inspection probe 30 is placed on a hat stringer with a large width, the probe 30 can separate into the first and second sides 46, 48. The first and second sides 46, 48 may be magnetically coupled to each other such as using magnetic coupling devices to support the first and second sides 46, 48 against the outside surface 16 of the hat stringer and prevent the first and second sides 46, 48 from separating more than the width of the hat stringer under inspection.
For ultrasonic inspection, a fluid, like water or air, can be fed through supply lines into channels on the inspection device to disperse the water between the device and the structure and to couple test signals between the inspection device and the structure. A fluid inlet 86 permits transfer of a fluid through the housing 82 to channels to disperse the fluid. The design of
Also, instead of contact members, a fluid bearing may be created by pumping a thin layer of fluid, like water or air, between the housing and the surface of the structure. A fluid bearing may further prevent scratching of the surface.
Even if the probe has a fluid bearing, it may also include one or more contact members. Skids may be beneficial for fluid bearing probes to prevent damage or marring of a surface of a structure when initially placing a probe on the structure or magnetically coupling two probes on opposite sides of the structure, particularly when the fluid bearing is not be in use.
The first inspection probe 210 may cooperate with a second inspection probe 211 as seen in
Probe 210 straddles the hat stringer to permit movement of the first probe 210 along the length of the hat stringer for inspection. Probe 211 is inside the hat stringer in the application of
As the inspection device moves along the length of the hat stringer, the probes 210, 211 may re-orient the magnetic coupling devices 42 and/or inspection sensors to the shape of the hat stringer such as to compensate for a change in the angle of the sides of the hat stringer.
The invention should not be limited to the specific disclosed embodiments. Specific terms are used in a generic and descriptive sense only and not for purposes of limitation.